Certain pollycyclic aromatic hydrocarbons are metabolized by ovarian enzymes to reactive products which destroy oocytes. Intraovarian injection of benzo (a) pyrene or derivatives of benzo(a)pyrene also produces oocyte destruction, suggestiong that ovarian metabolism is responsible for the observed ovotoxicity. Murine strain differences in sensitivity to ovotoxins disappear when mice are treated with a putative ultimate ovotoxin the 7,8-dihydrodiol-9,10-epoxide metabolite of benzo(a)pyrene by intraovarian injection. This suggests that differences in metabolic activation may be a major determinant in strain and species differences in response to ovotoxins. Oocyte destruction by polycyclic aromatic hydrocarbons is inherited as a polygenic trait and is not linked to the aromatic hydrocarbon responsiveness locus (Ah locus). Characterization of benzo( a)pyrene metabolites produced by ovarian enzymes suggests that metabolism in the 7,8,9,10 region may reflect more accurately the ability of the ovary to activate the parent compound to ovotoxic products.